The present invention lies in the field of micro-optical lenses as used in fiber optic data communication systems, whether singles or arrays, and particularly relates to inexpensive lenses that launch laser light into high-bandwidth optical fibers while reducing or eliminating feedback to the lasers.
A typical known arrangement is shown in FIG. 1, wherein an optical lens 10 is interposed between a laser (i.e. coherent) light source 15 and the front-end of an optical fiber 20. The laser source 15 is mounted on for instance from a transistor outline (TO) header or a circuit board or 12 that covers the open end of a cavity 14. The lens 10 has an object (or input) surface 25 and an image (or output) surface 30. The lens 10 is held in optical alignment with the laser source 15 by a transistor outline (TO) can or a molding 16. FIG. 1 shows, by ray tracing, the typical path of light from the laser source 15 into the front-end 22 of the fiber 20. The optical fiber 20 also has a back-end 24 that connects with a receiver device 35.
There are a number of antagonistic design considerations relating to such lenses. This includes the situation that the volume of space within a package containing the laser, lens and fiber end is very small. Typically there is only 300 xcexcm between the laser light source and the input surface of the lens in parallel optical channel applications. This places restrictions upon the lens design. Furthermore, such lens coupling units are often manufactured in an array (typically 12xc3x971). The most significant objective in the design of such lenses is the avoidance of back reflections. Referring again to FIG. 1, conventional fiber surface 22 partially reflects the input laser light, which will then interfere with the source light 15 (and thus the data represented by the modulated light source) resulting in data errors at the far-end of the optical fiber. It is also possible for partial reflection to occur at the output surface 24, to be propagated back towards the laser light source 15 again leading to data corruption. A further requirement is that lens launches the laser light in the fiber while avoiding the refractive index anomalies in the fiber center as well as those at the core-cladding interface thus improving the bandwidth of the data communication.
One example in the prior art of an approach to the problem of partial reflections is described in British Patent Publication No. GB 2 354 839 A (Agilent Technologies Inc). This prior art document describes the toroidal lens surfaces as replacement for earlier hyperbolic transfer lenses.
It is further known to use sub-micron diffraction patterns (eg small ridges as a lens surface in an effort to reduce back reflections. These lens surfaces are produced by use of expensive sub-micron wafer technologies and these lenses attenuate the laser beam.
It is generally desirable to be able to injection mold micro lenses since that fabrication process is well suited for manufacturing at high volumes and low cost. The lenses are required to retain their shape at temperatures of 200xc2x0 C. or above since laser transmitter/transceiver modules are exposed to high temperatures during their placement on PCB boards by a solder re-flow process or a solder bath. For this reason, only polymers with high glass transition temperatures can be used. However, the use of these types of polymer prevents the application of diffractive surfaces. Besides polymers, certain glass types can also be utilized, however this will significantly raise the price of the lens or lens array.
An optical lens that has at least one end surface of a surface shape that is the combination of a conic component, a spiral component and a cone component.
The lens can be arranged as an array. The lens or lens array can be integrated with a housing that has one end coupling for coupling to a laser source or laser sources and a further end for coupling to a free end of an optical fiber or fibers.
A method of fabricating the said optical lens involves forming a mold having the negative shape of the lens, including a mold portion corresponding to an end surface of the lens. The mold portion is the negative of the combination of a conic component, a spiral component and a cone component. The lens is produced by a flowable material applied to the mold.